The present invention relates generally to set retarding additives, set retarded hydraulic cementing compositions and methods of using the set retarded cement compositions for cementing subterranean zones including, but not by way of limitation, a subterranean zone that is penetrated by a well bore.
Hydraulic cement compositions are used for carrying out various operations in oil, gas and water wells including, but not limited to construction and completion operations such as primary cementing and remedial operations such as squeeze cementing. Primary cementing involves the placement of a hydraulic cement composition into the annular space between the walls of a well bore and the exterior of a pipe such as casing disposed therein. The cement composition is pumped into the annular space and allowed to set into an annular cement sheath therein whereby the pipe is bonded to the walls of the well bore by the set cement.
Squeeze cementing techniques usually involve the undesirable movement of oil, gas or water through small holes or cracks in pipe disposed in the well bore; holes, cracks, voids or channels in the annular cement sheath between the pipe and the well bore; annular spaces between the cement sheath and the pipe or the walls of the well bore and permeable zones or fractures in subterranean formations. Such holes, cracks, etc. are plugged by squeezing hydraulic cement compositions therein which harden and form impermeable plugs.
In performing cementing operations in such wells, the cement compositions are often subjected to high temperatures, particularly when the cementing is carried out in deep subterranean zones. The high temperatures can cause premature setting of the cement compositions, i.e., the compositions can not be pumped for long enough times before setting to place them in the zones to be cemented. This requires the use of set retarding additives in the cement compositions which extend the setting times of the compositions so that adequate pumping time is provided in which to place or displace the compositions into desired subterranean zones.
While a variety of cement set retarding additives have heretofore been developed and utilized, known additives can produce unpredictable results. Hydroxy carboxy acids, such as tartaric acid, gluconic acid and glucoheptonic acid are commonly used in oil well cementing as a cement retarder. However, if a slight excess of the hydroxy carboxy acid is used it can over-retard the set of the cement slurry thereby causing it to remain fluid for an extended period of time. This over-retardation will result in extended waiting time prior to resuming drilling and may allow gas to invade the slurry thereby causing unwanted gas migration. Additionally, prior art set retarding additives comprised of materials such as lignosulfonates and synthetic polymers are often expensive to produce.
Therefore, there is a need for improved set retarded cementing compositions and methods of cementing subterranean zones. In particular, there is a need for improved set retarding additives which are relatively inexpensive and bring about predictable cement composition setting times in subterranean environments encountered in wells.